Copper Foil for Printed Circuit

ABSTRACT

Disclosed is a copper foil for printed circuits prepared by forming a primary particle layer of copper on a surface of a copper foil, and then forming a secondary particle layer based on ternary alloy composed of copper, cobalt and nickel on the primary particle layer; in which the average particle size of the primary particle layer is 0.25 to 0.45 μm, and the average particle size of the secondary particles layer based on ternary alloy composed of copper, cobalt and nickel is 0.05 to 0.25 μm. Provided is a copper foil for printed circuits, in which powder fall from the copper foil can be reduced and the peeling strength and heat resistance can be improved by forming a primary particle layer of copper on a surface of a copper foil, and then forming a secondary particle layer based on copper-cobalt-nickel alloy plating on the primary particle layer.

TECHNICAL FILED

The present invention relates to a copper foil for printed circuits;more specifically relates to a copper foil for printed circuits, inwhich powder fall from the copper foil can be reduced and the peelingstrength and heat resistance can be improved, prepared by forming aprimary particle layer of copper on a surface of a copper foil, and thenforming a secondary particle layer based on copper-cobalt-nickel alloyplating thereon.

The copper foil for printed circuits of the present invention isparticularly suitable for, for example, a fine-pattern printed circuitand a FPC (Flexible Printed Circuit) for magnetic heads.

BACKGROUND ART

Copper and copper alloy foils (hereinafter referred to as “copper foil”)have contributed significantly to the advances in the electric- andelectronic-related industries and become essential, in particular, asmaterials for printed circuits. In general, a copper clad laminate isprepared by adhesively laminating a copper foil for printed circuitsonto a substrate such as a synthetic resin board or film under hightemperature and high pressure with or without using an adhesive. Then anecessary circuit is printed via the steps of resist application andexposure, followed by etching treatment for eliminating unwantedportions to form an intended circuit.

Finally, desired elements are soldered to form various types of printedcircuit boards for electronics devices. Although a treating method of acopper foil for printed circuit boards is different between a surface(roughened surface) to be bonded to the resin base material, and anon-bonding surface (glossy surface), a number of methods have been

For example, main requirements for the roughened surface formed on acopper foil include: (1) no oxidative discoloration during storage; (2)sufficient peel strength against a substrate even after high-temperatureheating, wet processing, soldering, chemical treatment and the like; and(3) no so-called lamination stains, which may occur after the laminationonto a substrate and etching treatment.

Roughening treatment of copper foil has an important role in determiningthe adhesiveness between the copper foil and the substrate. For thisroughening treatment, copper roughening treatment in which copper iselectrodeposited was initially employed, but then various othertechnologies have been proposed. Now, copper-nickel roughening treatmenthas become established as one of the representative treatment methods inorder to improve thermal peeling strength, hydrochloric-acid resistanceand oxidation resistance.

The present applicant has proposed copper-nickel roughening treatment(see Patent Document 1), and produced successful results. Acopper-nickel treated surface takes on a black color, and this blackcolor of the copper-nickel treated surface is now acknowledged as aproduct symbol of, in particular, rolled foil for flexible substrates.

The copper-nickel roughening treatment is superior in terms of thermalpeeling strength, oxidation resistance and hydrochloric acid resistance;but etching with an alkali etching solution, which has becomeincreasingly important for fine pattern treatment in recent years,becomes difficult, etch residues remain on the treated layer during theformation of fine patterns having 150 μm pitch or less.

Accordingly, for fine pattern treatment, the present applicantpreviously developed Cu—Co treatment (see Patent Document 2 and PatentDocument 3) and Cu—Co—Ni treatment (see Patent Document 4).

These roughening treatments showed better etching properties, alkalietching properties and hydrochloric-acid resistance, but it was foundthat thermal peeling strength was decreased when an acrylic adhesive wasused, and oxidation resistance was not sufficient as desired, and thecolor tone did not become black but was brown to dark brown.

Pursuant to the trend of finer patterns and diversification of printedcircuits in recent years, the followings are further required; 1)thermal peeling strength (particularly when an acrylic adhesive is used)and hydrochloric-acid resistance should be comparable to those for thecase of the Cu—Ni treatment, 2) etching with an alkali etching solutionshould be possible to produce a printed circuit having a pattern of 150μm pitch or less, 3) oxidation resistance should be improved (beingresistant to oxidation in an oven at 180° C. for 30 minutes) as in thecase of the Cu—Ni treatment, and 4) the treatment should produce a blacksurface as in the case of the Cu—Ni treatment.

In other words, when the circuit becomes finer, the circuit tends tomore easily peel off due to a hydrochloric acid etching solution, sothat such peeling off needs to be prevented. When the circuit becomesfiner, the circuit also tends to more easily peel off due to the hightemperature at a process such as soldering, so that such peeling offalso needs to be prevented. At the present time when circuits areincreasingly becoming finer, etching a printed circuit having a patternof 150 μm pitch or less with the use of, for example, a CuCl₂ etchingsolution is already an essential requirement, and alkali etching is alsobecoming a necessary requirement because resists and the like areincreasingly varied. A black surface is also becoming more importantfrom the viewpoint of manufacturing copper foil and chip mounting inorder to improve positioning precision and heat absorption.

In response to such demands, the present applicant successfullydeveloped a method of treating a copper foil, wherein a cobalt platedlayer or a cobalt-nickel alloy plated layer is formed on the copper foilsurface after being subject to copper roughening treatment via acopper-cobalt-nickel alloy plating, so that: the copper foil possessesmany of the above general properties as the copper foil for printedcircuits and particularly possesses the properties described above whichare comparable to those in the Cu—Ni treatment; thermal peeling strengthis not reduced when using an acrylic adhesive; the copper foil hassuperior oxidation resistance; and the copper foil surface takes on ablackened color (see Patent Document 5).

Preferably, after forming the cobalt plated layer or the cobalt-nickelalloy plated layer, rustproof treatment is applied, represented bycoating treatment with chrome oxide alone or coating treatment with themixture of chrome oxide and zinc and/or zinc oxide.

Subsequently, as the development of electronic equipment advances,semiconductor devices increasingly become smaller and more highlyintegrated. Even higher temperature is required for treatments in themanufacturing process of these printed circuits, and heat is generatedwhen using a product in which such semiconductor devices areincorporated. As a result, the decrease in bonding strength between acopper foil and a resin substrate is again recognized as a problem.

In light of the above, the present applicant inventively improvedthermal peeling resistance in the method for treating copper foil forprinted circuits according to Patent Document 5, in which a rougheningtreatment is performed to a surface of a copper foil by way ofcopper-cobalt-nickel alloy plating, and a cobalt plated layer or acobalt-nickel alloy plated layer is thereafter formed.

This method for treating copper foil for printed circuits is a method inwhich a cobalt-nickel alloy plated layer is formed after performing aroughening treatment to a surface of a copper foil viacopper-cobalt-nickel alloy plating, and then a zinc-nickel alloy platedlayer is further formed. It is an extremely effective invention, andmaterials produced according to the invention are now one of the majorproducts of copper-foil circuit materials.

For producing a copper-foil circuit that is even more thin-lined, theprocess of soft etching the upper surface of a copper circuit using anetching solution containing sulfuric acid and hydrogen peroxide isperformed after a circuit is once formed on a substrate. During thisprocess, a problem occurred that the etching solution infiltrated intothe edge portion of the bonded interface between the copper foil and aresin substrate such as polyimide.

This may be considered as a partial corrosion of the treated surface ofthe copper foil. Such corrosion is a significant problem since itreduces the bonding strength between the copper foil and the resin in afine circuit. Solving this problem is also demanded.

In the treatment of copper foil for printed circuits, in which acobalt-nickel alloy plated layer is formed after performing a rougheningtreatment to a surface of a copper foil via copper-cobalt-nickel alloyplating, and then a zinc-nickel alloy plated layer is further formed;the present inventors, after numerous attempts, successfully providedseveral major improvements in the properties of the copper foil forprinted circuits. The early technologies of the roughening treatment bycopper-cobalt-nickel alloy plating are disclosed in Patent Document 7and Patent Document 8.

However, since the structure of the roughening particles formed on thesurface of copper foil via copper-cobalt-nickel alloy plating as themost basic roughening treatment is dendritic, there was a problem thatthe particles came off from the upper or base parts of the dendriticstructure, causing a phenomenon generally known as powder fall.

This powder fall is a problematic phenomenon. Although a roughened layertreated by copper-cobalt-nickel alloy plating can be characterized byhaving superior adherence with a resin layer and superior heatresistance, the particles therein may easily come off by external forceas mentioned above, causing flaking due to “rubbing”, adhesion of flakesonto the roll, and occurrence of etch residues due to the flakes duringthe process.

Provided that blackening treatment by copper-cobalt-nickel alloy plating(in Example 1, Cu: 3.3 mg/dm², Co: 6.3 mg/dm², Ni: 1.6 mg/dm²) isperformed, techniques are disclosed in which copper foil is plated withfine copper particles in advance in order to make the color tone darkerin the blackening treatment and to prevent the phenomenon of powderfall, and in which a smooth layer of cobalt or cobalt-nickel is providedas the outermost layer to prevent powder fall (Patent Document 9 below).

In this case, providing a smooth layer of cobalt or cobalt-nickel as theoutermost layer is the main requirement for preventing powder fall.Rather, powder fall from copper-cobalt-nickel alloy plating will dependon the structure of particles in a primary layer of copper applied tocopper foil, and the composition and the particle structure of a cobaltlayer or a cobalt-nickel layer formed as a secondary particle layerthereon. However, the Patent Document 9 only provides formation of asmooth layer as the outermost layer, hardly providing a fundamentalsolution for powder fall.

-   Patent Document 1: Japanese Laid-Open Patent Publication No.    S52-145769-   Patent Document 2: Japanese Patent Publication No. S63-2158-   Patent Document 3: Japanese Patent Application No. H1-112227-   Patent Document 4: Japanese Patent Application No. H1-112226-   Patent Document 5: Japanese Patent Publication No. H6-54831-   Patent Document 6: Japanese Patent Publication No. 2849059-   Patent Document 7: Japanese Laid-Open Patent Publication No.    H4-96395-   Patent Document 8: Japanese Laid-Open Patent Publication No.    H10-18075-   Patent Document 9: Japanese Laid-Open Patent Publication No.    2004-260068

SUMMARY OF INVENTION Technical Problem

The object of the present invention is to provide copper foil forprinted circuits, which can: inhibit uneven treatment, and a phenomenoncommonly called as powder fall where roughening particles formed in adendritic structure via copper-cobalt-nickel alloy plating as the mostbasic roughening treatment come off from the surface of the copper foil;increase its peeling strength; and improve its heat resistance. As thedevelopment of electronic equipment advances, semiconductor devicesincreasingly become smaller and more highly integrated, and as a result,requirements for the treatments in manufacturing these printed circuitsare even more demanding. An object of the present invention is toprovide a technology which satisfies these demands.

Solution to Problem

The present invention provides the following inventions.

1) A copper foil for printed circuits prepared by forming a primaryparticle layer of copper on a surface of a copper foil, and then forminga secondary particle layer based on ternary alloy composed of copper,cobalt and nickel on the primary particle layer; wherein the averageparticle size of the primary particle layer is 0.25 to 0.45 μm, and theaverage particle size of the secondary particle layer based on ternaryalloy composed of copper, cobalt and nickel is 0.05 to 0.25 μm.2) The copper foil for printed circuits according to 1) above, whereinthe primary particle layer and the secondary particle layer areelectrodeposited layers.3) The copper foil for printed circuits according to 1) or 2) above,wherein the secondary particle is one or more dendritic particles grownon a primary particle.4) The copper foil for printed circuits according to any one of 1) to 3)above, wherein a bonding strength of the primary particle layer and thesecondary particle layer is 0.80 kg/cm or more.5) The copper foil for printed circuits according to any one of 1) to 3)above, wherein the bonding strength of the primary particle layer andthe secondary particle layer is 0.90 kg/cm or more.6) The copper foil for printed circuits according to any one of 1) to 5)above, wherein a roughness, Rz, of a surface formed by the primaryparticle layer and the secondary particle layer is 1.5 μm or less.7) The copper foil for printed circuits according to any one of 1) to 5)above, wherein a roughness, Rz, of a surface formed by the primaryparticle layer and the secondary particle layer is 1.0 μm or less.

The present invention can provide copper foil for printed circuits,prepared by forming a cobalt-nickel alloy plated layer on the secondaryparticle layer based on copper-cobalt-nickel alloy plating, and furtherforming a zinc-nickel alloy plated layer on the cobalt-nickel alloyplated layer.

The deposited amount of cobalt in the cobalt-nickel alloy plated layermay be set to 200 to 3000 μg/dm², and the ratio of cobalt may be set to60 to 66 mass %.

The zinc-nickel alloy plated layer can be formed in which the totalamount is set in the range of 150 to 500 μg/dm², the amount of nickel isset in the range of 50 μg/dm² or more, and the nickel ratio is set inthe range of 0.16 to 0.40.

A rustproof treatment layer may also be formed on the zinc-nickel alloyplated layer.

With regard to this rustproof treatment, for example, a coating layer ofchrome oxide alone, or a coating layer of the mixture of chrome oxideand zinc and/or zinc oxide may be formed. Furthermore, a silane couplinglayer may be formed on the mixed layer.

The copper foil for printed circuits described above may be used tomanufacture a copper-clad laminate in which the copper foil adheres on aresin substrate through thermocompression bonding without being mediatedby an adhesive.

EFFECTS OF INVENTION

The present invention provides copper foil for printed circuits, whichcan: inhibit a phenomenon commonly called as powder fall whereroughening particles formed in a dendritic structure viacopper-cobalt-nickel alloy plating as the most basic rougheningtreatment come off from the surface of the copper foil (the formation ofa secondary particle layer); increase its peeling strength; and improveits heat resistance.

Moreover, since an amount of abnormally grown particles will bedecreased, its particle size will be uniform, and its whole surface willbe covered; its etching properties will be improved, and formation of ahigh-precision circuit becomes possible.

As the development of electronic equipment advances, semiconductordevices increasingly become smaller and more highly integrated, and as aresult, requirements for the treatments in manufacturing these printedcircuits are even more demanding. The present invention can providetechnical effects to satisfy these demands.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 This is a schematic view showing the state of powder fall whenroughening treatment based on copper-cobalt-nickel alloy plating wasapplied on conventional copper foil.

FIG. 2 This shows a schematic view of a treated layer of the copper foilwith no powder fall according to the present invention, prepared byforming a primary particle layer on the copper foil, and then forming asecondary particle layer based on copper-cobalt-nickel alloy plating onthe primary particle layer.

FIG. 3 This shows a micrograph of the surface of the conventional copperfoil on which roughening treatment based on copper-cobalt-nickel alloyplating was applied.

FIG. 4 This shows a micrograph of the surface of the copper foil onwhich roughening treatment based on copper-cobalt-nickel alloy platingwas applied with a reduced current density and a decreased processingrate.

FIG. 5 This shows a micrograph of the treated layer of a copper foilwith no powder fall according to the present invention, which wasprepared by forming a primary particle layer on the copper foil, andthen forming a secondary particle layer based on copper-cobalt-nickelalloy plating on the primary particle layer.

FIG. 6 This shows a micrograph of the treated layer of a copper foilwith no powder fall according to the present invention, which wasprepared by forming a primary particle layer on the copper foil, andthen forming a secondary particle layer based on copper-cobalt-nickelalloy plating on the primary particle layer, and obtained by furtherimproving the roughness.

DESCRIPTION OF EMBODIMENTS

Copper foil used in the present invention may be either electrolyticcopper foil or rolled copper foil. In order to improve the peelingstrength of the copper foil after lamination, the surface of the copperfoil to be bonded to the resin base material, namely the roughenedsurface of the copper foil, is normally subject to roughening treatmentin which electrodeposition is performed onto the surface of a degreasedcopper foil to obtain a knobbed copper surface. Electrolytic copper foilshows irregularity at the time of manufacturing, but the convex portionsare reinforced by the roughening treatment to further emphasize theirregularity.

Rolled copper foil and electrolytic copper foil may be treated somewhatdifferently. As used in the present invention, “roughening treatment”includes such pretreatment and finishing treatments, and if desired, anyknown treatment related to copper-foil roughening.

This roughening treatment is to be performed herein usingcopper-cobalt-nickel alloy plating (in the following description, theroughening treatment based on copper-cobalt-nickel alloy plating iscalled “a secondary particle layer” to clearly distinguish it from theabove processes), but powder fall and the like would occur by simplyforming a copper-cobalt-nickel alloy plated layer on the copper foil asdescribed above.

FIG. 3 shows a micrograph of the surface of the copper foil on which acopper-cobalt-nickel alloy plated layer is formed. As shown in FIG. 3,fine particles grown in a dendritic structure are seen. Generally, thefine particles grown in a dendritic structure shown in FIG. 3 areproduced under high current density.

When treated under such high current density, particle nucleation isinhibited at the initial electrodeposition, causing new particlenucleation to be formed at the tips of the particles. As a result, thinand long particles will be gradually grown in a dendritic structure.

Therefore when electroplating is performed under lower current densityto prevent this, as shown in FIG. 4, there are less sharp projections,and more particles and roundly shaped particles are grown. Powder fallwill be improved to a smaller extent under the condition shown in FIG.4, which is, however, not enough to achieve the object of the presentinvention.

Powder fall is illustrated in FIG. 1 in the case that acopper-cobalt-nickel alloy plated layer is formed as shown in FIG. 3.This powder fall occurs because fine dendritic particles are formed oncopper foil as described above. These dendritic particles are easilybroken at their branches or come off at their root by external force.These fine dendritic particles may cause flaking due to “rubbing”, grimeon the roll due to the flakes, and etch residues due to the flakesduring the process.

In the present invention, a secondary particle layer based on ternaryalloy composed of copper, cobalt and nickel is to be formed on a primaryparticle layer which is formed on a surface of copper foil. Micrographsof the surface of copper foil on which these primary particles andsecondary particles are formed are shown in FIG. 5 and FIG. 6 (see belowfor details).

The obtained thereby is a copper foil for printed circuits, wherein aphenomenon commonly called as “powder fall” and uneven treatment;namely, flaking due to “rubbing” during the process, grime on the rolldue to the flakes, and etch residues due to the flakes; can beinhibited, its peeling strength can be increased, and its heatresistance can be improved.

As clearly shown in Examples below, optimal conditions to prevent powderfall are the average particle size of 0.25 to 0.45 μm for the primaryparticle layer, and the average particle size of 0.05 to 0.25 μm for thesecondary particle layer based on ternary alloy composed of copper,cobalt and nickel.

The primary particle layer and the secondary particle layer describedabove are formed by electroplating. This secondary particle ischaracterized by being one or more dendritic particles grown on aprimary particle.

As described above, the average particle size for the secondary particlelayer, which is set to as small as 0.05 to 0.25 μm, can also be restatedas the height of the particles. That is, one of the features of thepresent invention can be considered as inhibiting the height of thesecondary particle so that peel-off (powder fall) of the particles isinhibited.

The bonding strength of 0.80 kg/cm or more, even 0.90 kg/cm or more, canbe achieved for the primary particle layer and the secondary particlelayer formed as described above.

Moreover, with regard to the roughness of the surface formed by theprimary particle layer and the secondary particle layer, Rz of 1.5 orless, even 1.0 μm or less, can be achieved. Lowering surface roughnessinhibits a phenomenon of powder fall more effectively. The presentinvention can provide a copper foil for printed circuits having theproperties and characteristics as described above.

(Plating Conditions for the Primary Particles of Copper)

One example of plating conditions for the primary particles of copper isas follows.

Note that the plating conditions shown below are merely an example ofsuitable conditions and the average particle size of the primary copperparticles formed on the copper foil has a role in preventing powderfall. Therefore, as long as the average particle size falls into therange of the present invention, plating conditions are in no way limitedto the conditions shown below. The present invention will encompassthose.

Moreover, a metal plated layer may be provided between the copper foiland the primary particles before the primary particles are formed.Representative metal plated layers include a copper plated layer and acopper alloy plated layer. For providing a copper plated layer, themethods of forming the copper plated layer include electroplating whereonly an aqueous solution of copper sulfate containing copper sulfate andsulfuric acid as main components is used, and electroplating where anaqueous solution of copper sulfate combined with sulfuric acid, anorganosulfur compound having a mercapto group, a surface active agentsuch as polyethylene glycol, and also a chloride is used.

Solution composition: 10 to 20 g/L of copper, 50 to 100 g/L of sulfuricacidSolution temperature: 25 to 50° C.Current density: 1 to 58 A/dm²

Coulomb: 4 to 81 As/dm² (Plating Conditions for the Secondary Particles)

Note that, as described above, the plating conditions shown below aremerely an example of suitable conditions, the secondary particles is tobe formed on the primary particles, and the average particle size has arole in preventing powder fall. Therefore, as long as the averageparticle size falls into the range of the present invention, platingconditions are in no way limited to the conditions shown below. Thepresent invention will encompass those.

Solution composition: 10 to 20 g/L of copper, 5 to 15 g/L of nickel, 5to 15 g/L of cobaltpH: 2 to 3Solution temperature: 35 to 50° C.Current density: 24 to 50 A/dm²

Coulomb: 34 to 48 As/dm² (Plating Conditions to Form Heatproof Layer 1)

The present invention can further provide a heatproof layer to be formedon the secondary particle layer described above. The plating conditionsfor this are shown below.

Solution composition: 5 to 20 g/L of nickel, 1 to 8 g/L of cobaltpH: 2 to 3Solution temperature: 40 to 60° C.Current density: 5 to 20 A/dm²

Coulomb: 10 to 20 As/dm² (Plating Conditions to Form Heatproof Layer 2)

The present invention can further provide an additional heatproof layerto be formed on the secondary particle layer. The plating conditions forthis are shown below.

Solution composition: 2 to 30 g/L of nickel, 2 to 30 g/L of zincpH: 3 to 4Solution temperature: 30 to 50° C.Current density: 1 to 2 A/dm²

Coulomb: 1 to 2 As/dm² (Plating Conditions to Form a Rustproof Layer)

The present invention can further provide an additional rustproof layer.The plating conditions for this are shown below. Conditions forimmersion chromate treatment are shown below, but electrolytic chromatetreatment may also be used.

Solution composition: 1 to 10 g/L of potassium dichromate, 0 to 5 g/L ofzincpH: 3 to 4Solution temperature: 50 to 60° C.Current density: 0 to 2 A/dm² (for immersion chromate treatment)Coulomb: 0 to 2 As/dm² (for immersion chromate treatment)

(Types of a Weatherproof Layer)

An example may be application of an aqueous epoxy silane solution.

With regard to the copper-cobalt-nickel alloy plating as the secondaryparticles described above, a ternary alloy layer where 10 to 30 mg/dm²of copper, 100 to 3000 μg/dm² of cobalt, 50 to 500 μg/dm² of nickel aredeposited may be formed by electrolytic plating.

The heat resistance and etching properties would deteriorate when thedeposited amount of Co is less than 100 μg/dm². The deposited amount ofCo exceeding 3000 μg/dm² would not be preferred when magnetic effectsneed to be taken into account, and would cause etching stains andpossibly deterioration of acid resistance and chemical resistance.

The heat resistance would deteriorate when the deposited amount of Ni isless than 50 μg/dm². On the other hand, the etching properties woulddeteriorate when the deposited amount of Ni exceeds 500 μg/dm². That is,etch residues remain, and etching can be managed but fine patterningwill be difficult. The preferred deposited amount of Co is 500 to 2000μg/dm², and the preferred deposited amount of nickel is 50 to 300μg/dm².

Accordingly, the preferred deposited amount of copper-cobalt-nickelalloy plating can be 10 to 30 mg/dm² of copper, 100 to 3000 μg/dm² ofcobalt, and 50 to 500 μg/dm² of nickel. The above deposited amount ofeach component in the ternary alloy layer is a merely preferredcondition, and their ranges are in no way limited to those indicatedabove.

As used herein, etching stains mean that Co remains undissolved whenetched with copper chloride, and etch residues mean that Ni remainsundissolved when alkaline-etched with ammonium chloride.

In general, in order to form a circuit, an alkaline etching solution anda copper chloride-based etching solution are used as described in thefollowing Examples. Although these etching solutions and etchingconditions have broad utility, it is to be understood that conditionsare not limited to these conditions and any other conditions can beselected.

According to the present invention, a cobalt-nickel alloy plated layercan be formed on a roughened surface on which secondary particles wereformed (after being subject to roughening treatment) as described above.

For this cobalt-nickel alloy plated layer, the deposited amount ofcobalt is preferably 200 to 3000 μg/dm², and the ratio of cobalt ispreferably set to be 60 to 66 mass %. In a broad sense, this treatmentcan be considered as a type of rustproof treatment.

This cobalt-nickel alloy plated layer should be provided to an extentthat the bonding strength between the copper foil and the substrate isnot substantially reduced. The deposited amount of cobalt of less than200 μg/dm² would not be preferred because it would result in decreasedthermal peeling strength and deteriorated oxidation resistance andchemical resistance as well as a reddish treated surface.

In addition, the deposited amount of cobalt exceeding 3000 μg/dm² wouldnot be preferred when magnetic effects need to be taken into account,and would cause etching stains and possibly deterioration of acidresistance and chemical resistance. The preferred deposited amount ofcobalt is 400 to 2500 μg/dm².

Moreover, an excess amount of deposited cobalt might cause infiltrationduring soft etching. From this, the preferred ratio of cobalt can be 60to 66 mass %.

As described below, infiltration during soft etching is directly andmainly caused by a heatproof and rustproof layer comprising azinc-nickel alloy plated layer. Nonetheless, adjusting the amount ofcobalt as indicated above is preferred because cobalt may also causeinfiltration during soft etching.

On the other hand, an insufficient amount of deposited nickel woulddecrease thermal peeling strength, oxidation resistance, and chemicalresistance. Moreover, an excess amount of deposited nickel woulddeteriorate alkali etching properties. Therefore it is preferable todetermine in balance with the cobalt content.

The present invention can further provide a zinc-nickel alloy platedlayer to be formed on a cobalt-nickel alloy plating. The total amount ofthe zinc-nickel alloy plated layer is set to 150 to 500 μg/dm², and theratio of nickel is set to 16 to 40 mass %. It serves as a heatproof andrustproof layer. This is also merely a preferred condition, and otherknown zinc-nickel alloy platings can be used. It will be understood thatthis zinc-nickel alloy plating is a preferred complementary condition inthe present invention.

Even higher temperature is required in the manufacturing process ofprinted circuits, and heat is generated when using a product in whichprinted circuits are incorporated. For example, in the case of aso-called double-layer material where a copper foil and a resin arebonded by thermocompression, they are exposed to heat at a temperatureof 300° C. or higher upon being bonded. Even under such conditions, itis necessary to prevent a decrease in the bonding strength between thecopper foil and the resin substrate, and this zinc-nickel alloy platingis effective.

With the conventional art, in a fine circuit comprising a zinc-nickelalloy plated layer in a double-layer material where a copper foil and aresin are bonded by thermocompression, discoloration due to infiltrationoccurs at the edge portion of the circuit during soft etching. Nickelhas an effect to inhibit infiltration of an etching agent (an aqueousetching solution of H₂SO₄: 10 wt % and H₂O₂: 2 wt %) used during softetching.

As described above, by setting the total amount of a zinc-nickel alloyplated layer to 150 to 500 μg/dm², the nickel ratio in the alloy layerto 16 mass % at the lower limit and 40 mass % at the upper limit, andthe nickel content to 50 μg/dm² or more; the zinc-nickel alloy platedlayer comes to be able to serve as a heatproof and rustproof layer, andexert effects to inhibit infiltration of an etching agent used duringsoft etching and prevent a reduction in the bonding strength of acircuit due to corrosion.

When the total amount of the zinc-nickel alloy plated layer is less than150 μg/dm², the ability of heat resistance and rust-proofing isdecreased, and it becomes difficult to serve as a heatproof andrustproof layer. When the amount exceeds 500 μg/dm², resistance tohydrochloric acid tends to be deteriorated.

Moreover, when the nickel ratio in the alloy layer is less than 16 mass% at the lower limit, the amount of infiltration during soft etchingexceeds 9 μm, and it is not preferred. Technically, the upper limit of40 mass % for the nickel ratio is a limit value to allow formation of azinc-nickel alloy plated layer.

As described above, the present invention can provide, if needed, acobalt-nickel alloy plated layer and further a zinc-nickel alloy platedlayer in sequence to be formed on a copper-cobalt-nickel alloy platedlayer as a secondary particle layer. The total deposited amount ofcobalt and nickel in these layers may be adjusted. The total depositedamount of cobalt is preferably set to 300 to 4000 μg/dm², and the totaldeposited amount of nickel is preferably set to 150 to 1500 μg/dm².

When the total deposited amount of cobalt is less than 300 μg/dm², heatresistance and chemical resistance would deteriorate. The totaldeposited amount of cobalt exceeding 4000 μg/dm² might cause etchingstains. Moreover, when the total deposited amount of nickel is less than150 μg/dm², heat resistance and chemical resistance would deteriorate.The total deposited amount of nickel exceeding 1500 μg/dm² would causeetch residues.

Preferably, the total deposited amount of cobalt is 1500 to 3500 μg/dm²,and the total deposited amount of nickel is 500 to 1000 μg/dm². As longas the above conditions are satisfied, they are not limited to theparticular conditions described in this paragraph.

Then rustproof treatment is performed if desired. Preferred rustprooftreatment for the present invention is coating treatment with chromeoxide alone or coating treatment with the mixture of chrome oxide andzinc/zinc oxide. The coating treatment with the mixture of chrome oxideand zinc/zinc oxide is a treatment to form a rustproof layer based onthe zinc-chromium group mixture consisting of zinc or zinc oxide andchrome oxide by electroplating using a plating bath containing zinc saltor zinc oxide and chromate.

As the plating bath, representatively used is a mixed aqueous solutionof at least one from bichromate such as K₂Cr₂O₇ and Na₂Cr₂O₇, CrO₃, andthe like; at least one from water-soluble zinc salt such as ZnO andZnSO₄.7H₂O; and alkali hydroxide. Examples of representative platingbath compositions and electrolytic conditions are as follows.

Copper foil obtained in this manner will have superior thermal peelingstrength, oxidation resistance and hydrochloric acid resistance.Moreover, a CuCl₂ etching solution can be used to perform etching to theprinted circuits with a pattern of 150 μm pitch or less, and even alkalietching can be performed. Moreover, infiltration into the edge portionof a circuit during soft etching can be inhibited.

For a soft etching solution, an aqueous solution of H₂SO₄: 10 wt % andH₂O₂: 2 wt % can be used. Processing time and temperature can beadjusted appropriately.

As the alkali etching solution, for instance, a solution (temperature50° C.) consisting of NH₄OH solution with 6 mol/liter, NH₄Cl solutionwith 5 mol/liter, and CuCl₂ solution with 2 mol/liter is known.

Copper foils obtained from all the above processes show a black color asin the case of the Cu—Ni treatment. A black color is significant interms of higher positioning precision and heat absorptivity. Forexample, printed circuit boards including rigid and flexible boards aremounted with components such as IC, a resistor and a capacitor in anautomated process. In the process, chip mounting is performed whilereading a circuit by a sensor. At this time, positioning on the copperfoil treated surface may be performed through a film such as Kapton.Positioning when making a through hole is similarly performed.

The blacker the treated surface is, the better the light is absorbed,and therefore positioning will be more precise. Furthermore, whenmanufacturing a board, bonding is often performed while applying heat tothe copper foil and the film for curing. If heat is applied usinglong-wavelength radiation such as far-infrared and infrared radiation atthis time, heating efficiency is better when a treated surface takes ona blackened color.

Finally, if desired, for the primary purpose of improving the bondingstrength between the copper foil and the resin substrate, silanetreatment is performed where a silane coupling agent is applied onto atleast a roughened surface on the rustproof layer.

Silane coupling agents used for this silane treatment includeolefin-based silane, epoxy-based silane, acrylic silane, amino silaneand mercapto-based silane. Any agent appropriately selected among themmay be used.

A method for applying a silane coupling agent solution may be eitherspray by a sprayer, application by a coater, immersion, or flow coating.For example, Japanese Patent Publication No. S60-15654 describes theimprovement in the adhesive strength between a copper foil and a resinsubstrate by performing silane coupling treatment after applyingchromate treatment onto a roughened side of the copper foil. See thereference for details. Then, if desired, annealing treatment may beperformed in order to improve the ductility of copper foil.

EXAMPLES

Now reference is made to Examples and Comparative Examples. Please notethat these Examples are merely for illustrative purpose, and the presentinvention is not limited thereby. That is, other aspects ormodifications included in the present invention are encompassed.

Example 1 to Example 9

A primary particle layer (Cu) and a secondary particle layer(copper-cobalt-nickel alloy plating) were formed on rolled copper foilunder the conditions and ranges shown below.

Bath compositions and the plating conditions used herein are as follows.

[Bath Compositions and Plating Conditions] (A) Formation of a PrimaryParticle Layer (Cu Plating)

Solution composition: 15 g/L of copper, 75 g/L of sulfuric acid

Solution temperature: 35° C.

Current density: 2 to 58 A/dm²

Coulomb: 8 to 81 As/dm²

(B) Formation of a Secondary Particle Layer (Cu—Co—Ni Alloy Plating)

Solution composition: 15 g/L of copper, 8 g/L of nickel, 8 g/L of cobalt

pH: 2

Solution temperature: 40° C.

Current density: 24 to 31 A/dm²

Coulomb: 34 to 44 As/dm²

Comparative Example 1 to Comparative Example 9

In Comparative Examples, the bath compositions and the platingconditions used herein are as follows.

[Bath Compositions and Plating Conditions] (A) Formation of a PrimaryParticle Layer (Copper Plating)

Solution composition: 15 g/L of copper, 75 g/L of sulfuric acid

Solution temperature: 35° C.

Current density: 1 to 58 A/dm²

Coulomb: 4 to 81 As/dm²

(B) Formation of a Secondary Particle Layer (Cu—Co—Ni Alloy PlatingConditions)

Solution composition: 15 g/L of copper, 8 g/L of nickel, 8 g/L of cobalt

pH: 2

Solution temperature: 40° C.

Current density: 24 to 50 A/dm²

Coulomb: 34 to 48 As/dm²

For the primary particle layer (Cu plating) and the secondary particlelayer (Cu—Co—Ni alloy plating) on the copper foil formed according tothe above Examples, the average particle size of the primary particles,the average particle size of the secondary particles, powder fall,peeling strength, heat resistance and roughness (Rz) are shown in Table1.

The corresponding results from Comparative Examples are also shown inTable 1.

TABLE 1 Particle size of Height of secondary Peeling Heat Roughnessprimary particles particles strength resistance Rz (μm) (μm) Dust fall(kg/cm) (kg/cm) (μm) Comparative Example 1 0.15 0.05 Good 0.75 0.70 0.87Comparative Example 2 0.15 0.15 Good 0.75 0.70 0.88 Comparative Example3 1.5 0.25 Fair 0.83 0.72 0.90 Comparative Example 4 0.15 0.35 Bad 0.850.72 0.91 Example 1 0.25 0.05 Good 0.88 0.71 0.98 Example 2 0.25 0.15Good 0.90 0.72 0.98 Example 3 0.25 0.25 Fair 0.92 0.73 1.02 ComparativeExample 5 0.25 0.35 Bad 0.93 0.72 1.15 Example 4 0.35 0.05 Good 0.950.73 1.20 Example 5 0.35 0.15 Good 0.96 0.74 1.20 Example 6 0.35 0.25Fair 0.98 0.75 1.51 Comparative Example 6 0.35 0.35 Bad 0.98 0.73 1.50Example 7 0.45 0.05 Good 0.96 0.71 1.21 Example 8 0.45 0.15 Good 0.970.72 1.54 Example 9 0.45 0.25 Fair 0.98 0.74 1.60 Comparative Example 70.45 0.35 Bad 0.98 0.77 1.55 Comparative Example 8 0.25 0 Good 0.94 0.541.10 Comparative Example 9 0 0.60 Bad 0.90 0.73 0.78

As clearly shown in Table 1, the results from Examples according to thepresent invention are as follows.

In Example 1, the current density was set to 51 A/dm² and 2 A/dm², andthe coulomb was set to 72 As/dm² and 8 As/dm² to form primary particles,while the current density was set to 24 A/dm², and the coulomb was setto 34 As/dm² to form secondary particles.

Note that the current density and the coulomb to form primary particlesare in two steps because formation of primary particles usually requirestwo-step electroplating: i.e. a first step in which particle nucleationoccurs, and a second step in which nuclear particles are grown byelectroplating. The former is an electroplating condition for theparticle nucleation in the first step, and the latter is anelectroplating condition for growth of the nuclear particles in thesecond step. We will not mention this for each of the following Examplesand Comparative Examples, because it applies to all.

The results showed that the average particle size of the primaryparticles and that of the secondary particles were 0.25 μm and 0.05 μmrespectively, no powder fall was observed, the peeling strength underordinary state was as high as 0.88 kg/cm, the heat resistance (peelingstrength after heating at 180° C. for 48 hours) was as high as 0.71kg/cm, and the surface roughness Rz was 0.98 μm.

In Example 2, the current density was set to 51 A/dm² and 2 A/dm², andthe coulomb was set to 72 As/dm² and 8 As/dm² to form primary particles,while the current density was set to 28 A/dm², and the coulomb was setto 39 As/dm² to form secondary particles.

The results showed that the average particle size of the primaryparticles and that of the secondary particles were 0.25 μm and 0.15 μmrespectively, no powder fall was observed, the peeling strength underordinary state was as high as 0.90 kg/cm, the heat resistance (peelingstrength after heating at 180° C. for 48 hours) was as high as 0.72kg/cm, and the surface roughness Rz was 0.98 μm.

In Example 3, the current density was set to 51 A/dm² and 2 A/dm², andthe coulomb was set to 72 As/dm² and 8 As/dm² to form primary particles,while the current density was set to 31 A/dm², and the coulomb was setto 44 As/dm² to form secondary particles.

The results showed that the average particle size of the primaryparticles and that of the secondary particles were 0.25 μm and 0.25 μmrespectively, and some powder fall was observed at an insignificantlevel. The peeling strength under ordinary state was as high as 0.92kg/cm, the heat resistance (peeling strength after heating at 180° C.for 48 hours) was as high as 0.73 kg/cm, and the surface roughness Rzwas 1.02 μm.

In Example 4, the current density was set to 55 A/dm² and 3 A/dm², andthe coulomb was set to 77 As/dm² and 12 As/dm² to form primaryparticles, while the current density was set to 24 A/dm², and thecoulomb was set to 34 As/dm² to form secondary particles.

The results showed that the average particle size of the primaryparticles and that of the secondary particles were 0.35 μm and 0.05 μmrespectively, no powder fall was observed, the peeling strength underordinary state was as high as 0.95 kg/cm, the heat resistance (peelingstrength after heating at 180° C. for 48 hours) was as high as 0.73kg/cm, and the surface roughness Rz was 1.20 μm.

In Example 5, the current density was set to 55 A/dm² and 3 A/dm², andthe coulomb was set to 77 As/dm² and 12 As/dm² to form primaryparticles, while the current density was set to 28 A/dm², and thecoulomb was set to 39 As/dm² to form secondary particles.

The results showed that the average particle size of the primaryparticles and that of the secondary particles were 0.35 μm and 0.15 μmrespectively, no powder fall was observed, the peeling strength underordinary state was as high as 0.96 kg/cm, the heat resistance (peelingstrength after heating at 180° C. for 48 hours) was as high as 0.74kg/cm, and the surface roughness Rz was 1.20 μm.

In Example 6, the current density was set to 55 A/dm² and 3 A/dm², andthe coulomb was set to 77 As/dm² and 12 As/dm² to form primaryparticles, while the current density was set to 31 A/dm², and thecoulomb was set to 44 As/dm² to form secondary particles.

The results showed that the average particle size of the primaryparticles and that of the secondary particles were 0.35 μm and 0.25 μmrespectively, and some powder fall was observed at an insignificantlevel. The peeling strength under ordinary state was as high as 0.98kg/cm, the heat resistance (peeling strength after heating at 180° C.for 48 hours) was as high as 0.75 kg/cm, and the surface roughness Rzwas 1.51 μm.

In Example 7, the current density was set to 58 A/dm² and 4 A/dm², andthe coulomb was set to 81 As/dm² and 16 As/dm² to form primaryparticles, while the current density was set to 24 A/dm², and thecoulomb was set to 34 As/dm² to form secondary particles.

The results showed that the average particle size of the primaryparticles and that of the secondary particles were 0.45 μm and 0.05 μmrespectively, no powder fall was observed, the peeling strength underordinary state was as high as 0.96 kg/cm, the heat resistance (peelingstrength after heating at 181° C. for 48 hours) was as high as 0.71kg/cm, and the surface roughness Rz was 1.21 μm.

In Example 8, the current density was set to 58 A/dm² and 4 A/dm², andthe coulomb was set to 81 As/dm² and 16 As/dm² to form primaryparticles, while the current density was set to 28 A/dm², and thecoulomb was set to 39 As/dm² to form secondary particles.

The results showed that the average particle size of the primaryparticles and that of the secondary particles were 0.45 μm and 0.15 μmrespectively, no powder fall was observed, the peeling strength underordinary state was as high as 0.97 kg/cm, the heat resistance (peelingstrength after heating at 180° C. for 48 hours) was as high as 0.72kg/cm, and the surface roughness Rz was 1.54 μm.

In Example 9, the current density was set to 58 A/dm² and 4 A/dm², andthe coulomb was set to 81 As/dm² and 16 As/dm² to form primaryparticles, while the current density was set to 31 A/dm², and thecoulomb was set to 44 As/dm² to form secondary particles.

The results showed that the average particle size of the primaryparticles and that of the secondary particles were 0.45 μm and 0.25 μmrespectively, no powder fall was observed, the peeling strength underordinary state was as high as 0.98 kg/cm, the heat resistance (peelingstrength after heating at 180° C. for 48 hours) was as high as 0.74kg/cm, and the surface roughness Rz was 1.60 μm.

On the other hand, Comparative Examples showed the following results.

In Comparative Example 1, the current density was set to 47 A/dm² and 1A/dm², and the coulomb was set to 66 As/dm² and 4 As/dm² to form primaryparticles, while the current density was set to 24 A/dm², and coulombwas set to 34 As/dm² to form secondary particles.

The results showed that the average particle size of the primaryparticles and that of the secondary particles were 0.15 μm and 0.05 μmrespectively, and no powder fall was observed, but the peeling strengthunder ordinary state was as low as 0.75 kg/cm, and the heat resistance(peeling strength after heating at 180° C. for 48 hours) was also as lowas 0.70 kg/cm. In addition, the surface roughness Rz was as low as 0.87μm. This copper foil for printed circuits was evaluated as inferior ingeneral.

In Comparative Example 2, the current density was set to 47 A/dm² and 1A/dm², and the coulomb was set to 66 As/dm² and 4 As/dm² to form primaryparticles, while the current density was set to 28 A/dm², and coulombwas set to 39 As/dm² to form secondary particles.

The results showed that the average particle size of the primaryparticles and that of the secondary particles were 0.15 μm and 0.15 μmrespectively, and no powder fall was observed, but the peeling strengthunder ordinary state was as low as 0.75 kg/cm, and the heat resistance(peeling strength after heating at 180° C. for 48 hours) was also as lowas 0.70 kg/cm. In addition, the surface roughness Rz was as low as 0.88μm. This copper foil for printed circuits was evaluated as inferior ingeneral.

In Comparative Example 3, the current density was set to 47 A/dm² and 1A/dm², and the coulomb was set to 66 As/dm² and 4 As/dm² to form primaryparticles, while the current density was set to 31 A/dm², and thecoulomb was set to 44 As/dm² to form secondary particles.

The results showed that the average particle size of the primaryparticles and that of the secondary particles were 1.5 μm and 0.25 μmrespectively, powder fall was observed, the peeling strength underordinary state was as low as 0.83 kg/cm, and the heat resistance(peeling strength after heating at 180° C. for 48 hours) was 0.72 kg/cm,which was comparable to the levels of Examples. In addition, the surfaceroughness Rz was 0.90 μm. This copper foil for printed circuits wasevaluated as inferior in general.

In Comparative Example 4, the current density was set to 47 A/dm² and 1A/dm², and the coulomb was set to 66 As/dm² and 4 As/dm² to form primaryparticles, while the current density was set to 34 A/dm², and thecoulomb was set to 48 As/dm² to form secondary particles.

The results showed that the average particle size of the primaryparticles was 0.15 μm, and that of the secondary particles was as largeas 0.35 μm. Furthermore, a large amount of powder fall was observed. Thepeeling strength under ordinary state was as low as 0.85 kg/cm, and theheat resistance (peeling strength after heating at 180° C. for 48 hours)was 0.72 kg/cm, which was comparable to the levels of Examples. Inaddition, the surface roughness Rz was 0.91 μm. This copper foil forprinted circuits was evaluated as inferior in general.

In Comparative Example 5, the current density was set to 51 A/dm² and 2A/dm², and the coulomb was set to 72 As/dm² and 8 As/dm² to form primaryparticles, while the current density was set to 34 A/dm², and coulombwas set to 48 As/dm² to form secondary particles.

The results showed that the average particle size of the primaryparticles was 0.25 μm, and that of the secondary particles was as largeas 0.35 μm. Furthermore, a large amount of powder fall was observed. Thepeeling strength under ordinary state was 0.93 kg/cm, and the heatresistance (peeling strength after heating at 180° C. for 48 hours) was0.72 kg/cm, both of which were comparable to the levels of Examples. Inaddition, the surface roughness Rz was 1.15 μm. This copper foil forprinted circuits was evaluated as inferior in general.

In Comparative Example 6, the current density was set to 55 A/dm² and 3A/dm², and the coulomb was set to 77 As/dm² and 12 As/dm² to formprimary particles, while the current density was set to 34 A/dm², andthe coulomb was set to 48 As/dm² to form secondary particles.

The results showed that the average particle size of the primaryparticles was 0.35 μm, and that of the secondary particles was as largeas 0.35 μm. Furthermore, a large amount of powder fall was observed. Thepeeling strength under ordinary state was 0.98 kg/cm, and the heatresistance (peeling strength after heating at 180° C. for 48 hours) was0.73 kg/cm, both of which were comparable to the levels of Examples. Inaddition, the surface roughness Rz was 1.50 μm. This copper foil forprinted circuits was evaluated as inferior in general.

In Comparative Example 7, the current density was set to 58 A/dm² and 4A/dm², and the coulomb was set to 81 As/dm² and 16 As/dm² to formprimary particles, while the current density was set to 34 A/dm², andthe coulomb was set to 48 As/dm² to form secondary particles.

The results showed that the average particle size of the primaryparticles was 0.45 μm, and that of the secondary particles was as largeas 0.35 μm. Furthermore, a large amount of powder fall was observed. Thepeeling strength under ordinary state was 0.98 kg/cm, and the heatresistance (peeling strength after heating at 180° C. for 48 hours) was0.77 kg/cm, both of which were comparable to the levels of Examples. Inaddition, the surface roughness Rz was as large as 1.55 μm. This copperfoil for printed circuits was evaluated as inferior in general.

In Comparative Example 8, the current density was set to 51 A/dm² and 2A/dm², and the coulomb was set to 72 As/dm² and 8 As/dm² to form primaryparticles only, while no secondary particles were formed.

The results showed that the average particle size of the primaryparticles was 0.25 μm, no powder fall was observed, and the peelingstrength under ordinary state was 0.94 kg/cm, which was comparable tothe levels of Examples, but the heat resistance (peeling strength afterheating at 180° C. for 48 hours) was significantly reduced to 0.54kg/cm. In addition, the surface roughness Rz was 1.10 μm. This copperfoil for printed circuits was evaluated as inferior in general.

Comparative Example 9 shows a conventional example only having asecondary particle layer with no primary particle size. That is, forthis case, the current density was set to 50 A/dm², and the coulomb wasset to 25 As/dm² to form secondary particles.

The results showed that the average particle size of the secondaryparticles was as large as 0.60 μm, and a large amount of powder fall wasobserved. The peeling strength under ordinary state was 0.90 kg/cm, andthe heat resistance (peeling strength after heating at 180° C. for 48hours) was 0.73 kg/cm, both of which were comparable to the levels ofthe Examples. In addition, the surface roughness Rz was 0.78 μm. Thisrepresents an example having problems such as a large amount of powderfall, and thus this copper foil for printed circuits was evaluated asinferior in general.

As clearly shown by comparing Examples with Comparative Examplesdescribed above, the copper foil according to the present inventionprepared by forming a primary particle layer of copper on a surface ofthe copper foil, and then forming a secondary particle layer based onternary alloy composed of copper, cobalt and nickel on the primaryparticle layer, in which the average particle size of the primaryparticle layer is 0.25 to 0.45 μm and the average particle size of thesecondary particles layer based on ternary alloy composed of copper,cobalt and nickel is 0.05 to 0.25 μm, is found to be capable of havingsuperior effects to inhibit a phenomenon called powder fall and uneventreatment, increasing its peeling strength, and improving its heatresistance.

INDUSTRIAL APPLICABILITY

The object of the present invention is to provide copper foil forprinted circuits capable of having superior effects to inhibit uneventreatment and a phenomenon called powder fall in which rougheningparticles grown in a dendritic structure come off from the surface ofthe copper foil when forming a secondary particle layer composed ofcopper-cobalt-nickel alloy plating (roughening treatment), and furtherhaving increased peeling strength and improved heat resistance. Inaddition, since an amount of abnormally grown particles will bedecreased, its particle size will be uniform, and its whole surface willbe covered; its etching properties will be improved, and ahigh-precision circuit can be formed. Therefore, it is useful as aprinted circuit material for electronic equipments with increasinglydownsized and highly integrated semiconductor devices.

1. A copper foil for printed circuits prepared by forming a primary particle layer of copper on a surface of a copper foil, and then forming a secondary particle layer based on ternary alloy composed of copper, cobalt and nickel on the primary particle layer; wherein the average particle size of the primary particle layer is 0.25 to 0.45 μm, and the average particle size of the secondary particle layer based on ternary alloy composed of copper, cobalt and nickel is 0.05 to 0.25 μm.
 2. The copper foil for printed circuits according to claim 1, wherein the primary particle layer and the secondary particle layer are electroplated layers.
 3. The copper foil for printed circuits according to claim 2, wherein the secondary particle is one or more dendritic particles grown on a primary particle.
 4. The copper foil for printed circuits according to claim 3, wherein a bonding strength of the primary particle layer and the secondary particle layer is 0.80 kg/cm or more.
 5. The copper foil for printed circuits according to claim 4, wherein the bonding strength of the primary particle layer and the secondary particle layer is 0.90 kg/cm or more.
 6. The copper foil for printed circuits according to claim 5, wherein a roughness, Rz, of a surface formed by the primary particle layer and the secondary particle layer is 1.5 μm or less.
 7. The copper foil for printed circuits according to claim 5, wherein a roughness, Rz, of a surface formed by the primary particle layer and the secondary particle layer is 1.0 μm or less.
 8. The copper foil according to claim 1, wherein the secondary particle is one or more dendritic particles grown on a primary particle.
 9. The copper foil according to claim 1, wherein a bonding strength of the primary particle layer and the secondary particle layer is 0.80 kg/cm or more.
 10. The copper foil according to claim 9, wherein the bonding strength of the primary particle layer and the secondary particle layer is 0.90 kg/cm or more.
 11. The copper foil according to claim 1, wherein a roughness, Rz, of a surface formed by the primary particle layer and the secondary particle layer is 1.5 μm or less.
 12. The copper foil according to claim 1, wherein a roughness, Rz, of a surface formed by the primary particle layer and the secondary particle layer is 1.0 μm or less. 